Thursday, June 23, 2011

Strava Android App: head-to-head testing against Garmin Edge 500

This morning a head-to-head competition....

I had 8 minutes to catch Caltrain 206. Plenty of time, but no time to waste. I got my bike in the garage, turned on the Garmin, left the garage, shut the automatic door, then pulled my Android phone from my pocket, brought up the Strava app, and hit new ride.

Ten precious seconds later GPS signal was acquired and I quickly hit go. I clipped in and was off to the station.

Twice per block I checked the status of the Garmin. As I've noted, this is a GPS-challenged environment, and the Garmin doesn't like it. For the first three blocks the progress bar moved steadily to the right. Then it retreated a bit. Then it regained some of its previous progress... where it stalled.

I was doing well. Traffic was extremely light at 6:05 am, so my quest for scientific fairness wasn't placing too great a burden on my survival chances.

The train station is just south of 4th Street. When I reached 7th Street I missed the light. I stopped at the red. A few seconds later the Garmin switched to its main screen. Signal acquired! I hit start. There's not really a visual cue when start is hit, except in this case soon afterwards it said "timer paused". That meant, clearly, the timer had been successfully started. Since I wasn't moving it then went straight to auto-pause.

I continued the final three blocks to the station. I saw the Garmin clock switch from 6:06 to 6:07. As soon as I was off the bike I turned off the Garmin timer. I had plenty of time to put on my Speedplay cleat covers and walk to the platform inside the station before the 6:11 departure.

As I did so, I removed the phone and hit "stop", then "save". The ride was in the bank. Obviously the Garmin ride would need to wait until I arrived at work, since I don't have teathering required to connect my laptop, and can't connect the Garmin to the phone directly.

Results so far:
  1. speed:Android 10 seconds to acquire GPS, Garmin approximately 20 seconds more than one km. Android by a landslide
  2. Ease of use: The Android ride was safely in the bank by the time I stepped on the train. The Garmin was waiting until I get to work. As I type this I'm on the train passing Burlingame.
  3. Accuracy: From the phone display, the Android phone looks good. The phone display is simplified, however, using relatively long line segments which are clearly a numerical fit to the more detailed ride data. I need to wait until I can upload the ride to see how well it actually did. The Garmin data, or what data there is from the Garmin, needs to wait.

The phone does have the advantage of size over the Garmin. Bigger footprint = bigger antenna. GPS L5 band is at 1.17 GHz. Recall light travels at 30 cm per nanosecond, so that's a wavelength of 27 cm. I was never happy with antenna theory but from what I retained of it I'm pretty sure you'd like the antenna to be at least a quarter-wavelength in size, so if the antenna is less than 7 cm you're throwing away signal strength. My phone is 12 cm long by 6 cm wide while the Garmin is just 7 cm long by 4.5 cm wide. The phone is really too long and heavy for mounting on handlebars, even more so for a wrist (forearm straps are better but still cumbersome), so I think Garmin made a sound design decision here. The phone, on the other hand, has the advantage of a superior mounting point. But it definitely needs it: past experience shows the Garmin does not work when held in my hand.

Leaving Redwood City now... Menlo Park... Palo Alto.... Cal Ave.... Mt View. Time elapses.

Okay -- I looked at the data, and I'm impressed. First, most of the ride from the Android App:

Android full ride


Even though GPS is very challenging with thie buildings and hills of San Francisco, the Android app follows the roads without any obvious blips.

Here's a close-up of the end of the ride:

Android end of ride


You can see my track goes down the right side of Townsend, which is where I was riding, to the left of the parked cars, which is accurate... until I went onto the sidewalk and into the station.

Now here's what the Garmin reported. Recall due to the slow acquisition I got less than three blocks of data, so this is basically all I had with the Edge 500:

Garmin end of ride


Still not bad, although it has me passing now to the right of the parked cars, which was not my path. Is this statistically significant? Maybe, maybe not, but there's absolutely no evidence here the Android, despite being in my pocket rather than in the preferred mounting point of my bike stem (where the Garmin was), was in any way inferior.

When I got off the train in Mountain View I attempted a second experiment: Garmin Edge in one pocket, Android phone in the other. This was to try to reduce the confounding factor of placement. However, this experiment crashed and burned because when I moved the Edge 500 to my pocket (it was again slower on the acquisition, by the way) I must have accidently depressed the start-stop button, and the data were never recorded. With the Android phone this can't really happen, because I shut off the phone display before putting it into my pocket, and to turn off the data stream would require turning the display on, sliding my finger down the screen to unlock it, then hit the start-stop widget on the screen. This is all simple and quick if I want to do it, but is too complex for a mistake. On the other hand, it's easy to depress an external button.

At lunch I went for a run with the Android phone in my belt pouch. The run lasted around 80 minutes, so I was afraid the battery would be an issue, but it wasn't. And the results were great: here's the Strava record:



It was an out and back, much of the run on the Steven's Creek Trail. There's one minor glitch, but every other significant deviation of the outbound and inbound trajectory was real. Steven's Creek Trail has three dirt and gravel frontage trails along the segment I ran, and I can clearly see where I went onto and off these frontage trails. On the trail I tend to run from one side to the other depending on which appears to have better traction, so some of the variation in position was real. The only real downside was the inability to view the display when it was in my belt pouch and the lack of a "lap" button which I sometimes find useful. But it's clear that when running from work the Android phone is an excellent option, especially since I have such difficulty acquiring GPS signal with my Garmin near work.

So anyway, from these experiments all the evidence is, if anything, the Android phone is doing a better job than the Garmin Edge 500. The quick data acquisition is a great plus. The reduced battery life is an issue on longer events, the bigger weight is an issue in races, and the lack of a lap is an impediment for interval training, but otherwise it's working substantally better than I anticipated.

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